1. Field of the Invention
The present invention relates to a probe for measuring the oxygen concentration in a solution or a gas by utilizing quenching by oxygen of luminescence following excitation by light.
2. Description of the Prior Art
Heretofore, as for a method for measuring the oxygen concentration in an aqueous solution, there has generally and widely been used an electrochemical method in which an oxygen electrode represented by Clark type one is used and reduction current of oxygen is measured under a controlled electric potential. However, in this method, since an electric current which flows between two electrodes is measured, the current density cannot be so diminished, and therefore miniaturization of the electrodes to be used is limited. Further, an electric current is generated even in a small extent, and thus it is not proper from the safety aspect to use the method, for example in vivo or in a blood vessel.
In view of these problems, various methods utilizing light for measuring oxygen concentration have been proposed. Since it was reported that pyrenebutyric acid is effective as a fluorescent probe for measuring oxygen concentration (W. M. Vaugham and G. Weber, Biochem, 9, 464 (1970)), many researches have been conducted on probes utilizing quenching by oxygen of fluorescence from derivatives of pyrene. Further, another device utilizing pyrenebutyric acid was made (N. Opitz and D. W. Lubbers, Z. Biomed. Techn. 28 (31), (1983)). However, in this method it is necessary to use an ultraviolet ray as the exciting ray, so that materials which transmit an ultraviolet ray must be used in the optical system such as a conductor of the exciting ray. When a probe comprising perylene dibutyrate adsobed on silica gel is used, a visible ray (wave length of 468 nm) can be used as the exciting ray (J. I. Peterson, R. V. Fitzgerald and D. K. Buckhold, Anal. Chem. 56, 62 (1984)). However, since this probe greatly suffers from water, it is necessary to protect it with a hydrophobic and oxygen-permeable membrane, which makes the miniaturization thereof more difficult. Thus, there has not hithereto been a probe for measuring oxygen concentration where the exciting ray and luminescence are visible rays and which can stably be used even when it is directly immersed in a liquid to be examined without a protective membrane such as an oxygen-permeable membrane thereon.